1. Field of the Invention
This invention relates to new and useful improvements in non-aqueous pigment dispersions. It relates particularly to the transfer of a pigment from an aqueous pulp or presscake directly into organic vehicles by an operation known to those skilled in the art as flushing. It relates more particularly to agents for the flushing of an organic pigment to provide a low viscosity, shelf-stable dispersion having good tint strength.
2. Description of the Prior Art
The flushing of pigment presscakes, in order to disperse the pigment in an organic vehicle, is well known. The transfer may be effected in some cases by merely kneading the press cake and vehicle together until substantially all the water has separated. In most prior art methods, a surface-active agent is added to facilitate the transfer. There have been many attempts in the prior art to find different surface-active agents or surfactants, generally referred to as flushing aids, in order to solve specific problems such as the large amount of mechanical work required, a lack of tinting strength of the flushed color, and the like. Many attempts have been made to find a flushing aid for an organic pigment which would provide a flushed color having a low viscosity both initially and during long term storage. The search has been complicated by the further requirement that the flushing aid should have little or no detrimental effect on the tint strength of the flushed color.
Sulfonates prepared from various organic materials have been tried as flushing aids. Reference is made in U.S. Pat. No. 2,120,588 to the use of a condensation product of naphthalene sulfonic acid with formaldehyde. Petroleum sulfonates have long been used as dispersing agents in the flushing of pigment presscakes. In some instances, however the flushed color obtained has a high initial viscosity and a poor shelf stability, i.e., the viscosity increases to an unacceptably high value upon storage at ambient temperatures.
The use of cationic surface-active materials such as long-chain aliphatic quaternary ammonium, long-chain sulfonium, and long-chain phosphonium compounds as flushing aids, is taught in U.S. Pat. No. 2,192,954. In this patent, however, it is taught that such cationic material sometimes cause the formation of a water-in-oil emulsion which prevents the separation of the bulk of the water. In order to overcome that problem, U.S. Pat. No. 2,219,395 teaches the addition of a sulfonated fatty oil, a sulfonated aromatic compound or a fatty alcohol sulfate to the kneaded mass of pigment, water, oil and cationic material in order to reverse the objectionable water-in-oil emulsion.
U.S. Pat. No. 3,256,202 discloses improved surface-active agents including salts of sulfated hydrocarbon alcohols derived from sperm oil and suggests that they may be valuable as dispersants for dyes, pigments, etc. However, there is no disclosure of the use of sulfated or sulfonated sperm oils in a flushing process. Further, this patent is directed to mixtures of sulfated aliphatic hydrocarbon alcohols. These mixtures consist essentially of at least one salt of a sulfated lower aliphatic alcohol having from 1 to 4 carbon atoms and at least one salt of a sulfated higher aliphatic alcohol having at least 16 carbon atoms. Sulfated sperm oil is listed as one of the higher aliphatic alcohols. Mixture of the latter with the former is treated as essential to the invention.
U.S. Pat. No. 3,449,261 discloses a mixture of sulfonated hydrocarbons such as spermiceti oil and tris(butoxyethyl)phosphate in dyeing operations. However, the disclosure is for use in dyeing textiles as a low-foaming wetting agent for the textile and not as a flushing aid.
Accordingly, it is a purpose of the instant invention to provide for flushing an organic pigment whereby a flushed color having a low initial viscosity, good shelf stability, and good tint strength will be available to the printing ink and coating industries.